Aerosols or particles in suspension are the main source of attenuation of visible and infrared transmissions through the atmosphere. This has serious implications for many activities which range from landing aircraft to very sophisticated electrooptic applications for both military and civilian activities. A major difficulty with aerosols is that they are subject to large temporal and spatial fluctuations which make forecasting impossible and point measurements inadequate. Therefore, it is often necessary to continuously monitor the aerosol extinction over the complete spatial domain of interest in applications where their effects are potentially critical. This may mean, for example, measuring the aerosol extinction coefficient at a large number of points along the glide path of a landing aircraft because of important changes that occur with altitude.
The backscatter lidar has long been proposed to remotely measure atmospheric parameters since it has the required spatial and temporal resolutions and has proved very efficient in such specialized tasks as determining the concentration of trace gases. However, conventional lidar techniques have limitations and provide an unreliable technology to determine aerosol extinction coefficients since the measured backscatter signal is a function of two unknowns, i.e. the backscatter and the extinction coefficients.
Conventional lidar measurements alone, are insufficient to determine either one of these. Additional, independent, information on the nature of the aerosols and a consistent boundary value are necessary in order to resolve the indeterminacy. This would require additional measurements. Moreover, the lidar equation is nonlinear and its solutions are subject to instabilities. Furthermore, the standard lidar approach ignores the influence of multiple scattering.